Process for continuously refining metals,notably,pig-iron

ABSTRACT

The present invention concerns a process for continuously refining metals, particularly pig-iron in which one or several nozzles or tuyeres are mounted below the bath surface in one or several associated refining vessels, and a gaseous or liquid protective medium and oxygen are supplied separately through these nozzles. The protective medium consists of hydrocarbons or of hydrocarbonaceous substances.

United States Patent [191 Nilles et al. Apr. 2, 1974 [54] PROCESS FOR CONTINUOUSLY REFINING 2,855,293 10 1958 Savard et a1. .1 75/60 METALS, NOTABLY, PIGJRON 3,326,672 6/1967 Worner 3,634,065 1/1972 Worner [75] Inventors: PaulEmile Nilles, m g; J q 3,706,549 12 1972 Knuppel et a1. 75/60 Piret, Luttich, both of Belgium FOREIGN PATENTS OR APPLICATIONS [73] Asslgnee f l f f f 1,125,005 8 1968 Great Britain 75 46 503,446 6/1954 Canada 75/82 Sulzbach-Rosenberg, Germany [22] Filed: June 14, 1972 Primary ExaminerL. Dewayne Rutledge Assistant Examiner-M. J. Andrews 21 A l. N 2 2 9 1 pp 0 6 Attorney, Agent, of Firm+-Lawrence I. Field [30] Forelgn Appllcatlon Prlorlty Data ABSTRACT June 16, 1971 Belgium Aug. 10, 1971 Belgium 43391 The W invention concerns a Process for continuously refining metals, particularly pig-iron in which 52 us. c1 75/60, 75/46, 75/59 one or Several nozzles or wyeres are mounted below 51 1m. 01. c216 7/00 the bath Surface in one or Several associated refining [58] Field Of Search 75/46, 59, 60 vessels, and a gaseous or liquid Protecti"e medium and oxygen are supplied separately through these nozzles. 5 References Cited The protective medium consists of hydrocarbons or of UNITED STATES PATENTS hydrocarbonaceous substances.

2,862,810 12/1958 Alexandrovsky 75/60v 8 Claims, 5 Drawing Figures 7 /25' 1 2 13 l 1 LN-'7" F r 14 mENIEmPR 2:914

SHEET 2 BF 2 AIAVAV/AWIWJVA FIG.3

PROCESS FOR CONTINUOUSLY REFINING METALS, NOTABLY, PIG-IRON The present invention concerns a process for continuously refining metals, particularly pig-iron in which one or several nozzles or tuyeres are mounted below the bath surface in one or several associated refining vessels, and a gaseous or liquid protective medium and oxygen are supplied separately through these nozzles. The protective medium consists of hydrocarbons or of hydrocarbonaceous substances.

Continuous processes for the refining of metal baths including pig iron are known in the state of the art. The advantages of this procedure with respect to conventional, discontinuous operation, in the main are the following:

By eliminating the time intervals between loading and tapping, the continuity of the refining process leads to higher outputs and to increased reliability as regards products of constant quality. Further, a continuously running process may be monitored better and may be adjusted better. A continuous yield of refined metal may well lead to a more constant material-flow in the subsequent production stages and therewith to higher outputs.

Though these fundamental advantages of a continuous refining process are known, they have been adopted so far in industrial practice only to a very limited extent. Thus these processes are only at the testing stage in steelproduction, and they are not being used for large-scale steel production. To date the drawbacks of continuous refining processes have consisted in the difficulty of separating the individually successive stages of the refining process for both the slag and for the metal bath. Not least, raising and withdrawing of the required refining slags and a constant flow of material inside the refining vessel are being hampered by the supply of the refining gases, since these are being fed-in above the bath by means of lance-like arrangements.

Recently a process for refining pig iron to steel has been adopted in practice, according to which refining oxygen is blown together with a liquid or gaseous protective medium into a convertor underneath the bath surface, e.g., as described in British Pat. No. 1,253,581. By making use of a hydrocarbon or hydrocarbonaceous protective media when in a definite ratio to the oxygen, the feasibility is achieved of blowing oxygen into the metal bath and underneath the latters surface, without the oxygen-supply nozzles wearing faster than the surrounding walls. The amounts of the supplied protective media are suitably kept to below percent by weight with respect to'the amount of oxygen under conventional operational conditions. Thus an amount of 2-3 percent volume for propane and an amougtgf about 5 percent weight for fuel oil with respect to the amount of oxygen are appropriate.

In one aspect, the process according to the invention represents a combination between the continuous refining method and the feed oxygen nozzles, where the latter are being used as for the refining of pig iron, where oxygen is fed in below the surface of the bath. However, the continuous refining according to the invention, making use of those nozzles and of the special vessel shapes, does provide advantages of a surprising nature, while the drawbacks of the previous continuous processes arising from feeding-in the refining gases above the bath surface are eliminated.

One variation of this process consists in series arrangement of several refining vessels connected one to another and continuously being traversed by the molten metal. By series arrangement is meant, of course, a sequential one. In principle, this sequence may assume diverse geometric shapes, it might be a circle for instance. The refining gas preferably is oxygen, and is fed in through the nozzles which are mounted below the bath surface. The nozzles also allow passage to a protective medium which surrounds the oxygen jet but is kept separate from it and is fed in simultaneously. The protective medium is a hydrocarbon or a gaseous and/or liquid hydrocarbonaceous substance.

Special advantages are obtained by sequentially arranging several refining vessels to the extent that the continuous refining sequence may be sub-divided into several stages according to the number of such vessels. Extensive concentration-equalization between slag and bath may take place in each vessel. Thus a simple way is obtained in which to remove from the melt the materials present in the pig iron, for instance, sulfur and phosphorus, and to obtain a high metallurgical yield.

The additivies or fluxes forming slags and/or inducing cooling may in such a case be separately introduced in each refining vessel, or be tapped therefrom. The metal bath or melt proper continuously flows through these sequentially arranged vessels, preferably near the surface. A surprising advantage is so achieved: slag and melt do not emulsify as strongly as in known pig iron refining processesparticularly when bottom blowing- ,hence the slag holds less iron and a higher yield is obtained.

Arranging the nozzles below the surface of the bath may be achieved in diverse ways. The most obvious configuration is perpendicular to the metals direction of flow, in which case the nozzles and the gas fed in will only refine the melt, while metal flow must be initiated by other means such as inclines or gravity or other suit- ,able means, and must be maintained in like manner. If the nozzles are emplaced obliquely, preferably all in one direction and below the baths surface, then the entry impulse or kinetic energy from the gas may be used also for metal motion. By appropriately combining nozzles located laterally and in the bottom of the refining vessel, and by means of a suitable oblique-position of these nozzles, one may combine as desired motions for agitation and/or metal flow.

The slag-forming additives of fluxes may be introduced at diverse locations onto the melt and/or they may be fed into it together with the refining gas. Introducing slag-forming substances, particularly quick lime, near the discharge of the finished and refined metal has proved particularly advantageous. In this region of the continuous refining process, the fresh slag is characterized by very low amounts of undesirable associated metals and it may be moved in a direction opposite to that of the melt flow. From a metallurgical viewpoint, this kind of slag motion is optimal. On its way to the gate or pouring-in hole, it picks up more and more of the melt impurities and therefore becomes increasingly contaminated. Furthermore such slag motion for pig iron refining entails still another advantage, namely that of small iron proportion in the slag, since the slag encounters on its travel a constantly more reducing metal bath. Of course one must consider that when pig iron with low or high phosphorus content is being refined, the slag in this region is already being withdrawn from the partly reduced pig iron melt in which the silicon has been completely oxidized. Otherwise the pig iron continuously flowing into the refining vessel would again absorb a high proportion of the slags phosphorus.

According to the invention, the several refining vessels arranged sequentially may be of different sizes. It is advantageous that the first refining vessel, in which the major refining takes place, and into which the entire amount of cooling scrap is introduced, should be appreciably larger than the subsequent vessel(s). Another variation of the process according to the invention consists in carrying out the continuous refining within a single vessel. The latter preferably is fairly long in the direction of flow of the metal melt as compared to the transverse dimension. Below the bath surface such a vessel may be further sub-divided into one or more chambers. The oxygen nozzles are mounted in the bottom and/or in the lower part of the walls. Such a vessel shape is simpler to build and provides clear advantages when carrying or moving the slag in a direction opposite the direction of metal flow.

In this execution or embodiment, all chambers make up one part of a single vessel, the lateral walls of the latter consisting of the consecutive lateral walls of the chambers, and the end walls of the single vessel being made up of the end walls of the first chamber, or of the first and last for several chambers. The intermediate chamber walls along the direction of metal flow either terminate below the metal level or else are provided with corresponding open cross-sections for the metal bath so as to allow slag and metal to flow across the wall. Mounting the nozzles must take into account two considerations: in one case, the gas entry impulse should be used as a means for furthering the metal bath motion or flow; in the other case, equalization of concentration transversely and normally to this direction of flow of the metal must be provided for in the area of the nozzles.

' The invention will be further understood from the accompanying drawings illustrating various embodiments of the refining vessles according to the invention, in which:

FIG. 1 illustrates a section through one suitable refining vessel;

FIGS. 1A and 2B show vertical sections of FIG. 1, taken on planes A-A and B-B of FIG. 1;

FIG. 3 shows another embodiment;

FIG. 3A is an end view of the apparatus of FIG. 3; and

FIG. 4 shows still another embodiment.

The numerals in these Figures designate the followmg:

Numerals 1 through 5 designate the sequentially arrayed refining vessels with common bottom 6. Pouring in hole 7 allows continuous introduction of the metal 8 which is to be refined. Refined metal 10 discharges through orifice 9. Slag-forming substances 12 are fed in through conduit 11. Used up slag l4 discharges through orifice 13. Obliquely positioned nozzles 15 through 19 are mounted in bottom 6 and serve to introduce the refining gas, preferably oxygen. Cut-outs 20-23 in the intermediate walls allow exchanging slag and metal between neighboring vessels. An axle 26 may be rotated in order to empty all vessels simultaneously or to tilt them simultaneously or to repair them in case of difficulties.

FIG. 3 shows another illustrative embodiment for the refining process according to the invention. The metal flows toward the discharge side 31 in longitudinal refining vessel 27 into which the melt or charge 29 to be refined is introduced at 28. The refining gas, preferably oxygen, is surrounded by a protective medium and fed in through refining nozzles 30. The slag is added at 32 and flows in direction 33, opposite to that of metal melt 34. The slag is removed at 35.

FIG. 4 shows another variation of the refining vessel according to the process of the invention. In this case the bottom of vessel 36 consists of consecutive steps 37. Oxygen introduction nozzles 38, 39 and others are inclined in direction of metal flow and are built into the downwards-directed areas of steps 40, 41 and others.

We claim:

1. A process for continuously refining molten metal comprising:

introducing the metal to be refined into the entry end of an elongated refining vessel and forming a metal bath therein;

introducing slag forming agents into the discharge end of said vessel, said discharge end being opposite to said entry end;

introducing oxygen surrounded by a sheath of fluid hydrocarbon into the metal bath in the vessel, at a point below the surface of the bath and directed so as to cause said metal to flow from the entry end of said vessel toward the discharge end of said vessel, whereby the metal melt will flow opposite to the slag in said vessel, due to the kinetic energy of said oxygen;

continuously refining said metal as it traverses the length of said vessel;

withdrawing refined metal from the discharge end of said vessel;

and withdrawing slag from the entry end of said vessel.

2. A process according to claim 1 wherein said fluid hydrocarbons are introduced through an annular clearance of concentrically arrayed nozzles in order to act as protective media for the oxygen and to prevent premature back-burning of the oxygen feed-in nozzles with respect to the surrounding walls.

3. A process according to claim 2 wherein the protective media may contain solid fuel particles.

4. A process according to claim 1 wherein fresh slag is being continuously formed in the refining vessel and that this slag moves in a direction opposite to that of metal of the charge.

5. A process according to claim 1 wherein the refining vessel is a single refining container with the predominant dimension in the direction of motion of the metal melt and is provided with oxygen feeding nozzles along its entire length.

6. A process according to claim 1 wherein the oxygen is introduced through feed-nozzles mounted in the refining vessel so that the fiow caused by the oxygen entering the metal melt will in turn cause an equalization of concentration in the metal melt across the entire metal bath cross-section transversely to the direction of flow.

7. A process according to claim I wherein the oxygen is introduced through feed-nozzles mounted in the refining vessel so that the flow generated by the oxygen entering the metal melt will cause a drop in concentraranged in series and the metal flows continuously from the first of said series to the last of said series of refining vessels. 

2. A process according to claim 1 wherein said fluid hydrocarbons are introduced through an annular clearance of concentrically arrayed nozzles in order to act as protective media for the oxygen and to prevent premature back-burning of the oxygen feed-in nozzles with respect to the surrounding walls.
 3. A process according to claim 2 wherein the protective media may contain solid fuel particles.
 4. A process according to claim 1 wherein fresh slag is being continuously formed in the refining vessel and that this slag moves in a direction opposite to that of metal of the charge.
 5. A process according to claim 1 wherein the refining vessel is a single refining container with the predominant dimension in the direction of motion of the metal melt and is provided with oxygen feeding nozzles along its entire length.
 6. A process according to claim 1 wherein the oxygen is introduced through feed-nozzles mounted in the refining vessel so that the flow caused by the oxygen entering the metal melt will in turn cause an equalization of concentration in the metal melt across the entire metal bath cross-section transversely to the direction of flow.
 7. A process according to claim 1 wherein the oxygen is introduced through feed-nozzles mounted in the refining vessel so that the flow generated by the oxygen entering the metal melt will cause a drop in concentration of the metal-associated and reduced substances in the direction of the discharge orifice of the refining vessel to be maintained.
 8. A process according to claim 1 wherein the refining is conducted in at least two refining vessels arranged in series and the metal flows continuously from the first of said series to the last of said series of refining vessels. 